The concept of elastography has been studied for more than a decade. For breast cancer, check-ups using ultrasound based technology have been developed. A further approach uses magnetic resonance imaging to obtain an elastrographic imaging of tissue (cf. Manduca A, Oliphant T E, Dresner M A, et al, “Magnetic resonance elastrography: Non-invasive mapping of tissue elasticity”, Med Image Anal 2001; 5: 237-54). At the microscopic level, such imaging approaches are not feasible and a finer imaging is required to detect tiny vibrations in the tissue.
The recent development of optical coherence tomography (OCT) allows fast imaging of tissue. OCT has just recently been used for elastography (cf. Schmitt J, Opt. Express, 1998 Sep. 14: 3(6):199-211, “OCT elastography: imaging microscopic deformation and strain of tissue”; and Rogowska J I, Patel N A, Fujimoto J G, Brezinski M E, Heart 2004 May, 90(5): 556-62 “Optical coherence tomographic elastography technique for measuring deformation and strain of atherosclerotic tissues”; Liang-XI, Crecea V, Boppart S A, J. Biomed Opt, 2011 Apr. 16(4):221-233, “DYNAMIC OPTICAL COHERENCE ELASTOGRAPHY: A REVIEW”). In these approaches, the tissue is excited to vibration and the mechanical response of the tissue is measured by optical coherence tomography, which has led to the term “optical coherence elastography” (OCE).
In the field of eye care, Manapuram R K, Aglyamov S R, Monediado F M, Mashiatulla M, Li J Emelianiv S Y, Larin K V, J. Biomed Opt, 2012 October 17(10):100501, doi: 10.1117/1JBO.17.10.100501, “In vivo estimation of elastic wave parameters using phase-stabilized swept source optical coherence elastography” and Ford M R I, Dupps W J Jr, Rollins A M, Roy A S, Hu Z, J. Biomed Opt, 2011 January-February: 16(1):016005, doi: 10.1117/1.3526701, “Method for optical coherence elastography of the cornea”, propose to perform OCE at the cornea of the eye. The cornea is excited to mechanical vibrations by placing an ultrasonic probe directly onto the front-face of the cornea.
Detorakis E T I, Drakonaki E E, Tsilimbaris M K, Pallikaris I G, Giarmenitis S, Ophthalmic Surg Lasers Imaging, 2010 January-February, 41(1): 135-41, doi: 10.3928/15428877-20091230-24, “Real-time ultrasound elastographic imaging of ocular and periocular tissues: a feasibility study” also relate to OCE at the eye. In addition, U.S. Pat. No. 7,576,865 B1 discloses an endoscope performing OCT imaging. US 2011/0098572 A1 relates to an imaging probe for a biological sample, which probe includes an OCT probe and an ultrasound probe combined with the OCT probe in an integral probe package capable of providing by a single scanning operation images from the OCT probe and the ultrasound probe.
WO 2013/106385 A2 discloses a medical device and a method that enables determination of the elastic property of the cornea. An ultrasound probe is placed onto the front face of the cornea. The probe delivers ultrasonic energy to the cornea and measures the mechanical response of the cornea. U.S. Pat. No. 7,359,062 B2 discloses a high speed spectral domain OCT adapted for optical Doppler tomography for measuring in vivo blood flow dynamics and tissue structure.
Although the state of the art provides solutions for performing elastography of the cornea, no working solution exists for elastography of the retina. There are, however, diseases in which an elastography measurement of the retina might be of advantage. One of these diseases is the age-related macular degeneration (AMD). Under U.S. Pat. No. 8,616,071 the NIH recently granted a research grant relating to elastographic imaging of the retina in AMD, and Qi W I, Li R, Ma T, Li J, Kirk Shung K, Zhou Q, Chen Z, Appl Phys Lett, 2013 Sep. 2, 103(10): 103704, Epub 2013 Sep. 6, “Resonant acoustic radiation force optical coherence elstography”, discusses the possible application of resonant acoustic radiation force as an excitation source for OCE for AMD.
Accordingly, there is a need to perform OCE at posterior parts of the eye, e.g. parts located behind the cornea or even behind the iris of the eye.